LG 55LH90 Owner's Manual page 35

Screen Reset (Reset to original factory values)
Returns Position, Size, and Phase to the default factory settings.
This feature operates only in RGB-PC mode.
m
x
m
_o
z
m
c
m
z
m
c
-0
Select PICTURE.
Select Screen (RGB-PC).
Select Reset.
Select Yes.
3S